1. Field of the Invention
The present invention relates to a magnetic recording and reproducing apparatus which records and reproduces digital signals (video signals and audio signals) and is useful for narrowing track pitches.
2. Description of the Related Art
A recording pattern in a prior art magnetic recording and reproducing apparatus, used in a home VTR or the like, is defined to record data without a guard band in order to increase recording density, and to conduct aximuth record in order to reduce cross-talk between adjacent tracks. The data is reproduced by a reproducing head having a wider head width than a track pitch, while taking deviation due to curvature of tracking into consideration.
Tracking errors are detected by recording a pulse, representing a rotation phase of a head drum, as a control signal in a control track of a magnetic tape. The control track is located along longitudinal direction of the magnetic tape, separately from a video track for recording a video signal. In a reproduction mode, by comparing a phase of the reproduced control signal from the control track with a phase of the rotation pulse of the head drum tracking error may be detected. (See, for example, VTR Technology, by R. Takahaski, NHK, Oct. 20, 1980.)
On the other hand, in 8 mm video technologies, four low frequency tracking pilots of different frequencies are generated, and one of them is azimuth-recorded for each video track by frequency-multiplexing them with the video signal without a guard band. In the reproduction mode, a reproducing head having a wider head width than the track pitch is used and two low frequency pilots recorded on the two adjacent video tracks are detected for inspection of cross-talk from the adjacent video tracks, and the amplitude levels of the two low frequency pilots are compared to detect tracking error. (For example, as disclosed in "8 mm Video (1)" by A. Hirota, Technical Report of the Institute of Television Engineers of Japan, VR61-1, pp. 1-6 Feb. 23, 1984)).
However, in a recent apparatus which converts a video signal to a digital signal and records and reproduces it on and from a magnetic tape, a reduction of the track pitch is intended in order to reduce the size and the weight of the apparatus and extend the recording time.
Accordingly, when the prior art apparatus is applied to such a narrow track pitch apparatus, the following problems arise.
For example, in the above two examples of the prior art, the magnetic head width Tw is usually designed to be approximately 1.5 Tp, where Tp is the track pitch. Accordingly, a tracking margin is usually 0.5 Tp. As Tp is narrowed, the absolute value of the tracking margin reduces. As a result, expansion of the tracking margin or improvement of the tracking precision is required.
Where Tw is set to 2Tp to give a greater tracking margin, the tracking margin is expanded, but the magnetic head width which crosses the adjacent tracks increases. As a result, when the data is azimuth recorded and reproduced in the above two examples of the prior art, a disturbance signal from adjacent cross-talk increases and a higher signal-to-noise ratio (S/N) is required.
Where interoperable reproduction between apparatus having a very large track curvature is required, a variation of the tracking error increases and there is a risk that a next track to the adjacent track on which data has been azimuth-recorded may be reproduced. In this case, an azimuth loss may not be expected, and a disturbance signal by the cross-talk of the next track to the adjacent track increases and a further higher S/N is required.
Accordingly, it is not possible to widen the magnetic head width more than an appropriate width, and the tracking margin cannot be simply expanded.
In a tracking error detector which uses the prior art control track, the control reference signal is recorded on a control track, which is different from the video track. Accordingly, the linearity (curvature) of the video track cannot be detected and it is very difficult to improve the detection precision of the tracking error.